The development of an imaging method capable of measuring the increase in apoptosis early in the course of pro-apoptotic/anti-proliferative pharmacotherapies will accelerate the evaluation of experimental pre- clinical therapies and permit the personalization of established therapies in the clinic. The molecular basis for such an imaging method lies in the fact that as cells proceed along pathways to apoptosis or death, phosphatidylserine (PS), a lipid normally facing the cytoplasm, flips and faces the extracellular milieu. PS is an attractive target for imaging pharmacotherapy because (i) diverse pharmacotherapies have a common propensity to induce apoptosis, (ii) PS is an early and general marker of apoptosis and, (iii) PS can be imaged using annexin V, a protein that binds PS selectively and which has been used as a radiolabeled clinical diagnostic agent. Using fluorescent annexin V's, we have obtained important proof of principle data that the accumulation of fluorescent annexin V (38kDa) reflects the early response to anti-proliferative drug treatment in animal models of diverse diseases (cancer, arthritis). We have also shown that a magneto/optical annexin V (50 nm) can be used to image ischemia induced apoptosis by MRI in vivo. Though Tc-annexin V has been used for imaging chemotherapeutic response, clinical results to date are can be described as limited and mixed. The premise of this proposal is that annexin V based probes can be successfully used to image chemotherapy induced apoptosis, provided a vastly improved understanding of how annexin V binds to tumor and endothelial cells stressed by various chemotherapic agents in vitro is obtained. In addition, key variables regarding annexin V probe behavior in vivo must be understood, including elucidation of the cellular targets of these probes and determination of whether chemotherapy induced changes in tumor blood volume complicate the quantitation of the molecular marker, PS. This proposal will provide essential information regarding the interaction of annexin V probes with cells subjected to chemotherapeutic stress, and allow imaging apoptosis to realize its as yet unrecognized and vast potential. It will provide a basis for the selection pharmotherapeutic regimes based on the expression of a molecular marker upregulated on tumors undergoing treatment, indicating which regimes will be efficacious for specific individuals, and sparing many side-effect prone regimes which provide no benefit. [unreadable] [unreadable]